Effectively scanning of a document must be performed in two directions at right angles. Typically one of these directions of scanning is achieved by moving the document relative to a fixed scanning device or moving the scanning device relative to a stationary document. In moving platen photocopiers, the document is moved relative to a stationary scanner.
The need for actual scanning in the second perpendicular direction can be obviated in such a photocopier by causing a narrow strip of document perpendicular to the direction of movement of the document to be illuminated or at least exposed to a photosensitive surface which itself is moved relative to the position of the exposed image of the document so that as the document moves so also does the photosensitive surface so that each successive strip of the document is transformed into a corresponding electrostatic strip in the photosensitive surface on which the document is imaged. Typically the photosensitive surface is the external surface of a cylindrical drum which is rotated in synchronism with the movement of the platen so that an electrostatic image of the document is built up on the external surface of the drum.
Moving platen copiers suffer from certain disadvantages not least of which is the need to secure the document which is to be copied securely on the surface of the platen so that the document does not move during movement of the platen. This means that books and delicate documents may well be crushed or damaged and clearly it would be an advantage to provide for fixed platen type copying for all such documents.
It is, therefore an object of the present invention to provide apparatus by which a moving platen copier can be converted into a fixed platen copier.